Add tar.gz compression support

[kevinschaper]

We should add support for uncompressing a tar.gz and (for now at least) ingesting all of the files inside.

This need comes from the Panther RefGenomeOrthologs.tar.gz file, which is actually just a single file within a tar gz (which is a little odd).

We could also consider whether it would instead make sense to have an option in kghub downloader to uncompress. Either would solve the problem, I think.